Dispersible carbon nanotubes and method for preparing same

Abstract

Dispersible single-walled and multi-walled carbon nanotubes (CNTs) are prepared by dissolving surfactants in water to form a solution; adding carbon nanotubes to the solution to form a mixture; sonicating and agitating the mixture to form a carbon-nanotube/water dispersion; centrifuging the dispersion to remove un-dispersed carbon nanotubes and impurities; repeatedly freezing and heating the CNT dispersion; and, sublimating water in the CNT dispersion by freezing and evacuating the dispersion to obtain carbon nanotubes coated with surfactant. The carbon nanotubes prepared by the method of the invention are dry, amphiphilic, and surfactant-coated powders that can be dispersed in both aqueous and organic solvents to form stable and uniform dispersions having a high concentration of carbon nanotubes.

1. A method for producing surfactant-treated carbon nanotubes comprising:
 dissolving a surfactant in an aqueous solvent to produce a solution; 
 adding carbon nanotubes to the solution to produce a mixture; 
 agitating the mixture to produce an aqueous dispersion of carbon nanotubes; 
 freezing the aqueous dispersion; 
 thawing the frozen aqueous dispersion; 
 removing water from the aqueous dispersion to produce powdered, surfactant-treated carbon nanotubes. 
 
     
     
       2. A method as recited in  claim 1  further comprising removing un-dispersed carbon nanotubes from the aqueous dispersion. 
     
     
       3. A method as recited in  claim 2  wherein removing un-dispersed carbon nanotubes from the aqueous dispersion comprises centrifuging the aqueous dispersion. 
     
     
       4. A method as recited in  claim 1  wherein agitating the mixture comprises sonicating the aqueous dispersion. 
     
     
       5. A method as recited in  claim 4  wherein the sonicating is performed at a power level of about 2 kilowatts per liter of aqueous dispersion. 
     
     
       6. A method as recited in  claim 1  wherein removing water from the aqueous dispersion comprises sublimating water from the frozen aqueous dispersion. 
     
     
       7. A method as recited in  claim 6  wherein the sublimating is performed at sub-ambient pressure. 
     
     
       8. A method as recited in  claim 6  wherein the sublimating comprises freezing the dispersion in liquid nitrogen followed by evacuating at a temperature of about −40° C. and a pressure less than 10 Pa for about 12 to about 24 hours. 
     
     
       9. A method as recited in  claim 1  further comprising repeatedly freezing and thawing the aqueous dispersion. 
     
     
       10. A method as recited in  claim 1  further comprising heating the thawed aqueous dispersion. 
     
     
       11. A method as recited in  claim 10  wherein the heating elevates the temperature of the aqueous dispersion to between about 50° C. to about 60° C. 
     
     
       12. A method as recited in  claim 1  wherein the surfactant comprises polyvinylpyrrolidone. 
     
     
       13. A method as recited in  claim 12  wherein the polyvinylpyrrolidone has a molecular weight between about 8,000 and about 1,300,000. 
     
     
       14. A method as recited in  claim 12  wherein the concentration of the polyvinylpyrrolidone in the aqueous solution is between about 0.05 and about 10 weight percent. 
     
     
       15. A method as recited in  claim 1  wherein the surfactant comprises polyvinylpyrrolidone and polyethylene glycol alkylphenyl ether. 
     
     
       16. A method as recited in  claim 15  wherein the concentration of the polyvinylpyrrolidone in the aqueous solution is between about 0.05 and about 10 weight percent and the concentration of the polyethylene glycol alkylphenyl ether is between about 0.05 and about 5 weight percent. 
     
     
       17. A method as recited in  claim 1  wherein the surfactant comprises polyvinylpyrrolidone and polyethylene glycol sorbitan monolaurate. 
     
     
       18. A method as recited in  claim 17  wherein the concentration of the polyvinylpyrrolidone in the aqueous solution is between about 0.05 and about 10 weight percent and the concentration of the polyethylene glycol sorbitan monolaurate is between about 0.05 and about 5 weight percent. 
     
     
       19. A method for dispersing carbon nanotubes in a liquid comprising:
 dissolving a surfactant in an aqueous solvent to produce a solution; 
 adding carbon nanotubes to the solution to produce a mixture; 
 agitating the mixture to produce an aqueous dispersion of carbon nanotubes; 
 freezing the aqueous dispersion; 
 thawing the frozen aqueous dispersion; 
 removing water from the aqueous dispersion to produce powdered, surfactant-treated carbon nanotubes; and, 
 dispersing the powdered, surfactant-treated carbon nanotubes in a liquid. 
 
     
     
       20. A method as recited in  claim 19  wherein the liquid comprises a solvent selected from the group consisting of: water, acetic acid, 1,4-butanediol, butanol, butylamine, chloroform, cyclohexanol, diethylene glycol, dimethyl acetamide, dimethylformamide, dimethyl sulfoxide, ethanol, ethylene diamine, ethylene glycol, formic acid, glycerin, isopropanol, methanol, methylene chloride, methylcyclohexanone, N-methylpyrrolidone, polyethylene glycol 400, propanol, propylene glycol, pyrrolidone, triethanolamine and vinylpyrrolidone.